1. Field of the Invention
the present invention relates to an optical film, and more particularly, to an optical film for collecting and refracting light.
2. Discussion of the Related Art
in general, a backlight unit provides light to a display device. FIG. 12 is a side view of a related art backlight unit in which an optical film is installed. As shown in FIG. 12, a backlight unit 10 uses a light source 15 to provide light to the display panel 17 of a display device, such as a thin film transistor liquid crystal display (TFT-LCD). The backlight unit 10 shown in FIG. 12 also includes an optical film 11 for collecting and refracting light emitted from the light source 15 so as to cause the refracted light to be incident upon the display panel 17. Furthermore, the backlight unit 10 can include a reflector 19 below the light source 15 as well as other adjacent optical films 13 and 14 above and below the optical film 11.
FIG. 13 is a perspective view of the related art optical film. The related art optical film 11 has a surface with a plurality of linear prism patterns 12 each having a triangular cross-section and positioned adjacent to each other. Since such a related art optical film 11 having the linear prism patterns 11, there is a limitation as to the directions from which light can be collected and refracted. Because of this limitation, there is a disadvantage in that the brightness of the display panel 17 is significantly lowered as a viewing angle of the display panel 17 increases.
FIG. 14 is a perspective view of a pair of related art optical films. To overcome the disadvantage of brightness decreasing as the viewing angle increases, a technique has been developed in which two sheets of optical films 21a and 21b having linear prism patterns with triangular cross sections 22a and 22b are positioned such that their prism patterns 22a and 22b perpendicularly cross each other, as shown in FIG. 14. Because the linearly arranged prism patterns 2a and 22b cross each other, the directions from which light is collected and refracted are increased. Accordingly, a decrease in brightness as the viewing angle of the display panel 17 increases is significantly reduced.
Although the directions in which light is collected and refracted is increase, there still is a limitation on the light-refracting direction due to the structure of the triangular prism patterns 22a and 22b. Thus, there is a problem in that overall brightness does not increase and may decrease overall brightness. The linearly arranged prism patterns 22a and 22b crossing each other cause a wet-out phenomenon due to optical coupling of uppermost tips of the prism patterns 22a of the lower optical film 21a with the upper optical film 21b and by the lower optical film 21a with another adjacent film. This causes a problem in that moire is produced in an image displayed on the display panel 17.
Moreover, there is no light scattering in the related art in which the two sheets of optical films 21 and 21b are positioned such that their linearly arrange prism patterns 22a and 22b cross each other due to the limited amount of light-refracting direction. Thus, there is a disadvantage in that if a mote or scratch is occurs between the optical films 21a and 21b during a manufacturing process, such a defect will be readily apparent. Accordingly, there is a problem in that productivity can lowered due to increased defects and working difficulty.